The following discussion of the prior art is intended to present the invention in an appropriate technical context and allow its significance to be properly appreciated. Unless clearly indicated to the contrary, however, reference to any prior art in this specification should be construed as an admission that such art is widely known or forms part of common general knowledge in the field.
Chemically, “Apixaban” is known as 4,5,6,7-tetrahydro-1-(4-methoxyphenyl)-7-oxo-6-[4-(2-oxo-1-piperidinyl)phenyl]-1H-pyrazolo[3,4-c]pyridine-3-carboxamide or 1-(4-methoxyphenyl)-7-oxo-6-[4-(2-oxo-1-piperidinyl)phenyl]-4,5,6,7-tetrahydro-1H-pyrazolo[3,4-c]pyridine-3-carboxamide of Formula (I).

International (PCT) Publication No. WO 2003/026652 A1 (the WO '652 A1) discloses the process for the preparation of pyrazole-pyridine derivatives. U.S. Pat. No. 6,967,208, the family equivalent of WO '652 A1 discloses apixaban, has utility as a factor Xa inhibitor, and is developed for oral administration in a variety of indications that require the use of an antithrombotic agent. The US '208 discloses isolation of apixaban using column chromatography. The purity of apixaban obtained by the process disclosed in US '208 is very low and not suitable for pharmaceutical uses. This fact is further confirmed by recent reports in World Journal of Pharmaceutical Science Vol. 3(3), Pg. 663-677 (2015) wherein the purity of 90-93% by HPLC was reported.
U.S. Pat. Nos. 7,005,435 B2, 6,989,391 B2, 6,995,172 B2, 7,338,963 B2, 7,371,761 B2, 7,531,535 B2, 7,691,846 B2 and 7,960,411 B2 disclose various analogues compounds of apixaban. All the patents are incorporated herein by reference in their entirety.
International (PCT) publication No. WO 2003/049681 A2 and its corresponding U.S. Pat. Nos. 6,919,451 B2 and 7,153,960 B2 disclose process for the preparation of apixaban and other pyrazole-pyridine derivatives.
International (PCT) publication No. WO 2007/001385 A2 and its corresponding U.S. Pat. No. 7,396,932 B2 (the US '932 B2) discloses the process for the preparation of pyrazole-pyridine derivatives as depicted in scheme-1. The US '932 B2 also disclose crystalline Form N-1 and Form H2-2 of apixaban alongwith the unit cell data thereof.

Wherein, Z is selected from Cl, Br, I, OSO2Me, OSO2Ph, and OSO2Ph-p-Me; ring D is selected from phenyl, 2-fluorophenyl, 3-chlorophenyl, and 4-methoxyphenyl;    R1a is selected from CH3, CH2CH3, CH2CH2CH3, OCH3, OCH2CH3, OCH2CH2CH3, OCH(CH3)2, OCH2CH2CH2CH3, OCH(CH3)CH2CH3, OCH2CH(CH3)2, OC(CH3)3, O-phenyl, OCH2-phenyl, OCH2CH2-phenyl, and OCH2CH2H2-phenyl;    R is selected from Cl, Br, and I; ring A is substituted with 0-1R4; B is NO2.
International (PCT) Publication No. WO 2003/048081 A2 and WO 2003/048158 A1 discloses the process for the preparation of pyrazole-pyridine derivatives by reacting the 3-morpholino-1-(4-nitrophenyl)-5,6-dihydropyridin-2(1H)-one and (Z)-ethyl 2-chloro-2-(2-(4-chlorophenyl)hydrazono)acetate to obtain pyrazole-pyridine derivative as depicted in scheme-2.

Journal of Labelled Compounds and Radiopharmaceuticals Vol. 54 (8) Pg. 418-425 (2011) discloses a nine-step synthesis for the preparation of [14C]apixaban with the label in the central lactam ring and three-step synthesis for the preparation of [14C]apixaban with the label in the outer lactam ring starting from 4-nitroaniline.
CN 102675314 A discloses the process for the preparation of apixaban by cyclization of p-nitroaniline with 5-chlorovaleroyl chloride or 5-bromovaleroyl chloride; the resulting 1-(4-nitrophenyl)-2-piperidinone underwent dichlorination with phosphorus pentachloride followed elimination; the resulting 3-chloro-5,6-dihydro-1-(4-nitrophenyl)-2(1H)-pyridinone underwent reaction with ethyl (2Z)-chloro[(4-methoxyphenyl)hydrazono]acetate; the resulting ethyl 4,5,6,7-tetrahydro-1-(4-methoxyphenyl)-6-(4-nitrophenyl)-7-oxo-1H-pyrazolo[3,4-c]pyridine-3-carboxylate underwent reduction followed by cyclization with 5-chlorovalaroyl chloride or 5-bromovalaroyl chloride; the resulting intermediate underwent amidation to give apixaban.
Journal of Medicinal Chemistry (2007), 50(22), 5339-5356 discloses the process for the preparation of apixaban and other derivatives. The reaction scheme-7 in the reference article discloses the preparation of compound 47a which is outlined herein scheme-3.

U.S. Patent Application Publication No. 2007/0203178 A1 discloses crystalline solvates of apixaban viz. dimethyl formamide solvate DMF-5 and formamide solvate Form FA-2 of apixaban characterized by unit cell parameters.
International (PCT) Publication No. WO 2011/0106478 A2 discloses a composition comprising crystalline apixaban particles having a mean particle size equal to or less than about 89 μm and a pharmaceutically acceptable diluent or carrier.
International (PCT) Publication No. WO 2012/0168364 A1 discloses a process for the preparation of apixaban via novel intermediate and crystalline form α of apixaban which is designated as sesquihydrate having water content between about 4.5 and 6.5%. The crystalline form α of apixaban is characterized by x-ray powder diffraction (XRD) and differential scanning calorimetry (DSC).
International (PCT) Publication No. WO 2013/119328 A1 discloses crystalline Form-I, Form-II and Form-III of apixaban.
International (PCT) Publication No. WO 2013/164839 A2 discloses an amorphous form of apixaban and process for the preparation and composition thereof.
U.S. PG-Pub. No. 2013/0245267 A1 discloses an amorphous form of apixaban and process for its preparation.
International (PCT) Publication No. WO 2014/056434 A1 discloses the crystalline form and the amorphous form of apixaban.
World Journal of Pharmaceutical Science Vol. 3(3), Pg. 663-677 (2015) discloses the detailed analysis of first synthetic method for the preparation of apixaban, alternative method for the preparation of apixaban, study of impurities during the preparation of apixaban and study of polymorphic forms which is incorporated herein in its entirety.
American Journal of Analytical Chemistry, Vol. 6, Pg. 539-550 (2015) discloses development and validation of stability indicating RP-HPLC method on core shell column for determination of degradation and process related impurities of apixaban which is incorporated herein in its entirety.
In view of the above, the present invention provides a process for the preparation of apixaban having higher particle size distribution suitable for formulations with crystalline Form N-1 and having lower level of one or more impurities.